Koi find their way, I assume by human hand, into many of Japan's seemingly haphazard waterways, catchments, ponds, and concrete rivers.
I wonder who decides to introduce Koi into a catchment like this? What time requirements does it take? Do they need permission from the city? Which leads to the question, is this even city property? (It was next to a shrine, it could have been on their property although it appears to be city infrastructure.) If someone illegally introduces koi into a place like this, what actions are taken by the city?